Coating material for non-porous and semi-porous substrates

ABSTRACT

A substrate coating is provided for application in association with ink jet ink imaging on the substrate. The coating enhances permanence of black and specialty non-black color ink jet prints. The coating material of the present invention can be applied to any non-porous or semi-porous substrate as a pre-print coating. The coating comprises a combination of two polymers, and DMEA to discourage adverse interaction between the two polymers.

TECHNICAL FIELD

The present invention relates to ink jet printing and, moreparticularly, to the application of black and color inks to a specialtycoated substrate for achieving enhancement in permanence and imagequality.

BACKGROUND ART

In continuous ink jet printing, ink is supplied under pressure to amanifold region that distributes the ink to a plurality of orifices,typically arranged in a linear array(s). The ink discharges from theorifices in filaments which break into droplet streams. The approach forprinting with these droplet streams is to selectively charge and deflectcertain drops from their normal trajectories. Graphic reproduction isaccomplished by selectively charging and deflecting drops from the dropstreams and depositing at least some of the drops on a print receivingmedium while other of the drops strike a drop catcher device. Thecontinuous stream ink jet printing process is described, for example, inU.S. Pat. Nos. 4,255,754; 4,698,123 and 4,751,517, the disclosures ofeach of which are totally incorporated herein by reference.

Achieving improvement in permanence and darkness of ink jet printremains a top priority in the printing business. For ink jet business togrow in the non-porous and semi-porous substrate arts, such as printingon metals and plastics, significant improvement in water resistance,print quality, and print adhesion of the image must be demonstrated.

Dye-based aqueous inks have not been suitable for printing on metals orplastics, due to their inherent high surface tension and their inabilityto wet non-porous substrates. Even when the surface tension is loweredenough to improve wetting, the ink does not stick to the surface, due tolack of surface penetration. Non-porous and semi-porous substrates havebeen resistant to dye-based aqueous inks because the print image is notsuitably waterfast, and is not resistant to smudging or bleeding. Onlysolvent inks can produce rub-fast images on these surfaces, but with theinherent disadvantage of high volatile organic compounds, safety andhealth concerns.

It is seen then that there is a need for an improved method ofoptimizing waterfastness and minimizing smudging and bleeding ofenvironmentally safe aqueous, black or non-black, dye-based inks, whenprinted on non-porous or semi-porous substrates.

SUMMARY OF THE INVENTION

This need is met by the coating material according to the presentinvention, wherein enhancement in permanence of black and specialtynon-black color ink jet prints, resistant to smudging and bleeding, isachieved. With the coating material of the present invention, non-porousmaterials, such as plastic and metal, can be printed with aqueous inkwhen the surface is precoated with the coating material. The coatingmaterial combines an acrylic polymer with polyethyleneimine (PI) orethoxylated polyethyleneimine (EPI), and uses DMEA to discourageinteraction between the two polymers. A mixture of alcohol and MEK canbe used for drying.

In accordance with one aspect of the present invention, a coatingmaterial for application on a non-porous or semi-porous substrate foruse with an ink jet printing system comprises an acrylic polymercombined with a polyethyleneimine polymer, and DMEA to prevent adverseinteraction between the two polymers. When the coating material isapplied to the non-porous or semi-porous substrate, waterfast prints areproduced which are resistant to smudging or bleeding when subjected tomoisture.

Other objects and advantages of the invention will be apparent from thefollowing description and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The present invention proposes a coating material for application on anon-porous or semi-porous substrate. The application occurs beforeprinting, as a pre-coat, using any suitable application means such asspraying. The coating material is particularly advantageous for use on anon-porous or semi-porous substrate, such as metal or plastic. Thesubstrate coating enhances the permanence of ink jet imaging on thesubstrate to produce waterfast prints resistant to smudging or bleedingeven when subjected to moisture.

In accordance with the present invention, the coating compositioncomprises an acrylic polymer combined with a polyethyleimine orethoxylated polyethyleimine polymer. Acrylic polymers are known to beeffective film formers on a variety of non-porous substrates. However,due to the anionic nature of acrylic polymers, such polymers are a poordye fixative, since the dyes in ink jet inks are also anionic. A betterfixative for ink jet ink dyes are a polyethyleimine or ethoxylatedpolyethyleimine polymer. PI and EPI are strong cationic polymers.Therefore, PI and EPI are capable of fixing the ink jet ink dye,rendering it insoluble and waterfast.

It would appear, therefore, that an acrylic polymer could be combinedwith PI or EPI in a pre-coating fluid, to result in a fixed dye withgood adhesion to a non-porous substrate. Unfortunately, such a mixtureproduces and immediate white precipitate due to the opposite charge ofthe polymers.

In accordance with the present invention, an acrylic polymer can becombined with PI or EPI to produce a stable coating fluid. Inparticular, a specified amount of DMEA is used in the coating fluid toprevent the adverse interaction between the two polymers in the coatingfluid.

The following example illustrates a stable formulation for the coatingfluid of the present invention.

EXAMPLE 1

Aqueous acrylic polymer 45.0% 30% solution DMEA 5.0% EthoxylatedPolyethyleneimine 5.0% 37% solution Denatured Alcohol 15.0% MEK 30.0%

EXAMPLE 2

Aqueous acrylic polymer 45.0% 30% solution DMEA 4.0% Polyethyleneimine,50% solution 4.0% Denatured Alcohol 17.0% MEK 30.0%

There is no difference in permanence and image quality of ink applied toa non-porous or semi-porous substrate coated with the composition ofExample 1 as compared to a pre-coat of Example 2. That is, when theunethoxylated polyethyleneimine is used rather than ethoxylatedpolyethyleneimine, the performance of the ink applied to the pre-coatedsurface is comparable.

In Example 1, the aqueous acrylic polymer can be any commerciallyavailable acrylic polymer, such as a 30% aqueous acrylic polymer IJX8154-99, available from Westvaco. In a preferred embodiment of theinvention, the acrylic polymer comprises styrene acrylic copolymer. TheEPI in Example 1 can be any suitable commercially available EPI, such asLupasol SC-61B, available from BASF as a 37% solution. In Example, 2,the PI is commercially available from Aldrich as a 50% solution. In bothExamples 1 and 2, the coating fluid made in accordance with the listedcomponents was stable.

EXAMPLE 3

Denatured Alcohol 50.0% Ethoxylated Polyethyleneimine 5.0% 37% solutionMEK 45.0%

Coating made according to Example 3 was stable. However, when applied toaluminum and plastic substrates, then imaged with 1036 ink, the printshad no permanency and washed off with water. This implies that theacrylic polymer component is needed for film formation and adhesion. Ina preferred embodiment, the acrylic polymer comprises styrene acryliccopolymer.

EXAMPLE 4

Aqueous acrylic polymer 45.0% 30% solution DMEA 5.0% EthoxylatedPolyethyleneimine 5.0% 37% solution MEK 45.0%

When denatured alcohol was removed from the composition, as is shown byExample 4, the resulting mixture was cloudy, and separated into twolayers. This implies that the alcohol adds the necessary means to keepthe components in the solution.

EXAMPLE 5

Aqueous acrylic polymer 50.0% 30% solution EthoxylatedPolyethyleneimine, 5.0% 50% solution Denatured Alcohol 45.0%

The coating solution formulated in accordance with Example 5 wasinitially cloudy, then a white precipitate formed at the bottom of thecontainer. Apparently, without the inclusion of DMEA, the anionic andcationic polymers interact, to the detriment of the purpose of thecoating solution. Furthermore, it appears that the amount of DMEA mustexceed 2% of the solution, as the inclusion of just 2% DMEA stillresulted in a cloudy, separating mixture, thereby not preventing theadverse interaction of the polymers.

To determine the effectiveness of the solutions in each example above,different types of non-porous or semi-porous substrates, such asaluminum foil and plastic credit cards, were precoated with solutions ofeach Example, followed by markings and drawdowns with 1036 black aqueousink. The images produced were evaluated for permanency to wet and dryrub.

Actual application of the coating fluid can be by any suitable means,such as a sprayer, followed by actual printing on a suitable printer.The sprayed and imaged substrate prints were evaluated forwaterfastness, bleed, and print intensity. The following chart compareswaterfastness and print quality with and without the pre-coat of Example1, where the substrates were imaged with 1036 black inks by drawdowns.

Plastic Credit Cards

precoat and ink only ink waterfastness 92% 8% print quality goodcoverage mottled

UV Coated Glossy Substrate

precoat and ink only ink waterfastness 96% 31% print quality averagecoverage extreme mottling

CD Plastic Pockets

precoat and ink only ink waterfastness 94% 12% print quality goodcoverage extreme mottling

Aluminum Foil

precoat and ink only ink waterfastness 96% 0% print quality goodcoverage mottled

Aluminum Plate

precoat and ink only ink waterfastness 99% 0% print quality goodcoverage mottled

From these results, it is seen that a sufficient amount of DMEA has theadvantage of preventing adverse interaction that occurs between the twopolymers when DMEA is not present. This, in turn, enhances waterfastnessof the image, producing prints that are resistant to dry or wet rub. A45% solvent mixture of alcohol and MEK is selected as a preferredformulation to speed up drying, therefore not requiring a dryer to drythe coated surface before imaging, and to enhance wetting. When alcoholwas eliminated and 45% MEK was used, the fluid was not stable andactually separated into distinct layers. When DMEA and MEK wereeliminated from the formulation of Example 1, the fluid was again notstable and it separated into distinct layers. In a preferred embodiment,addition of as high as 5% DMEA is necessary to keep the cationic chargeon the EPI at a minimum, thereby discouraging interaction with theacrylic polymer, until the coated surface is imaged with the aqueousink.

Therefore, in a preferred embodiment of the present invention, theaqueous coating solution comprises 5–10% (on 100% basis) of EPI at a 37%solution or PI at a 50% solution, and a minimum of 5% % of DMEA. Theacrylic polymer can comprise styrene acrylic copolymer, in an amount ofabout 20% to 50%, and preferably 45%, by weight of a 30% weight basis. Apreferred embodiment further comprises both MEK and alcohol. Alcoholacts as a better solvent than MEK for components in the coating, whileMEK is better than alcohol in etching the substrate, for betterpenetration of the fluid into the surface of the substrate. A ratio ofMEK to alcohol is selected to provide stability of the coating fluid andoptimum adhesion to the substrate, with a suitable ratio of MEK toalcohol in a preferred embodiment being about 2 to 1.

The coating solution may be applied by any suitable means, such as, forexample, by spraying, roller arrangement, or application by a printheadpositioned inline with the ink-applying printheads. When a printhead isused to apply the coating solution, the option exists of covering onlythe printed image area with the coating material, rather than the entirearea of the substrate. After application of the image, the print can bedried, such as with a heat gun, to set the image.

Pre-coat application can provide the advantage of eliminatingcolor-to-color bleed during imaging, since the dyes are fixedinstantaneously as the ink contacts the pre-coated substrate.Furthermore, with pre-coating, images appear darker and have sharperedge definition, since the coating minimizes ink penetration and allowsmore fixed dyes on the surface. Finally, complete drying of thepre-coated substrate may not be necessary. Therefore, drying can beapplied once after imaging, resulting in considerable savings in energy.

Imaging can be done on a continuous web, wherein the substrate issubjected to the coating material of the present invention. Imaging canbe accomplished on a moving bindery line, for example, with theprinthead positioned at a 90 degree angle to the substrate. The variouscolor heads are positioned behind each other so that they imagesequentially on the substrate as it passes underneath the head. In orderto obtain high quality color images, multiple drops of each color inkare printed at each pixel location. The jet spacing is 240–300 dpi withan orifice diameter of 0.7 to 0.9 mil. The stimulation frequency is 100kHz and all heads are synchronized.

As will be obvious to anyone skilled in the art, the components thatcomprise the coating are commercially available. It is also understoodand known in the art that waterfastness is dye specific, resulting invariations in the amount of waterfastness achieved, particularly whenvarying the inks being applied to the substrate. Almost all ink jet inksapplied on a variety of commodity substrates give vastly varying imagequality. Differences occur in optical density, brilliance, permanence,drying and dot resolution. The substrate coating composition of thepresent invention is particularly adaptable for printing permanentimages on non-porous and semi-porous substrates, such as metals andplastics. It will also be obvious to those skilled in the art thatadditional optional additives can be included in the formulation withoutdeparting from the scope of the invention. For example, additionaloptional additives can include fluorosurfactants such as Zonyl, tofurther enhance wetting, and a biocide to keep the fluid bacteria free.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatmodifications and variations can be effected within the spirit and scopeof the invention.

1. A coating fluid for enhancing permanence of ink jet imaging onnon-porous and semi-porous substrates, the coating fluid consistingessentially of a polyethyleimine or an ethoxylated polyethyleiminepolymers, an acrylic polymer, dimethylethanolamine in an amountsufficient to prevent interaction between the polymers, and a mixture ofmethyl ethyl ketone and alcohol.
 2. A coating fluid as claimed in claim1 wherein the coating fluid comprises an ethoxylated polyethyleneiminepolymer.
 3. A coating fluid as claimed in claim 2 wherein theethoxylated polyethyleneimine comprises from about 1.11 % to 3.7% byweight.
 4. A coating fluid as claimed in claim 3 wherein the ethoxylatedpolyethyleneimine comprises 1.85% by weight.
 5. A coating fluid asclaimed in claim 1 wherein the coating fluid comprises apolyethyleneimine polymer.
 6. A coating fluid as claimed in claim 5wherein the polyethyleneimine comprises from about 1.5% to 5.0% byweight.
 7. A coating fluid as claimed in claim 6 wherein thepolyethyleneimine comprises 2.0% by weight.
 8. A coating fluid asclaimed in claim 1 wherein the acrylic polymer comprises styrene acryliccopolymer.
 9. A coating fluid as claimed in claim 8 wherein the styreneacrylic copolymer is present in an amount of about 6.0% to 15.0% byweight.
 10. A coating fluid as claimed in claim 9 wherein the styreneacrylic copolymer comprises 13.5% by weight.
 11. A coating fluid asclaimed in claim 1 wherein the dimethylethanolamine is present in anamount of about 3% to 8% by weight.
 12. A coating fluid as claimed inclaim 11 wherein the dimethylethanolamine comprises 5% by weight.
 13. Acoating fluid as claimed in claim 1 wherein the alcohol is present in anamount of about 10% to 20% by weight.
 14. A coating fluid as claimed inclaim 13 wherein the alcohol is present in an amount of about 15% byweight.
 15. A coating fluid as claimed in claim 1 wherein the methylethyl ketone is present in an amount of about 20% to 50% by weight. 16.A coating fluid as claimed in claim 15 wherein the methyl ethyl ketoneis present in an amount of about 30% by weight.
 17. A method of formingan ink jet image comprising providing a non-porous or semi-poroussubstrate, precoating on the substrate a coating fluid comprising apolyethyleimine or an ethoxylated polyethyleimine polymers, an acrylicpolymer, dimethylethanolamine in an amount sufficient to preventinteraction between the polymers, and a mixture of methyl ethyl ketoneand alcohol; and subsequently ink jet printing an image onto thesubstrate.
 18. An imaged element comprising a non-porous or semi-poroussubstrate, a coating on the substrate, said coating comprising apolyethyleimine or an ethoxylated polyethyleimine polymer, an acrylicpolymer, and dimethylethanolamine in an amount sufficient to preventinteraction between the polymers; and a printed ink jet image appliedafter the substrate coating.
 19. A coating fluid for enhancingpermanence of ink jet imaging on non-porous and semi-porous substrates,the coating fluid comprising a polyethyleimine or an ethoxylatedpolyethyleimine polymer, an acrylic polymer, dimethylethanolamine in anamount sufficient to prevent interaction between the polymers, and amixture of methyl ethyl ketone and alcohol, wherein thedimethylethanolamine is present in an amount of about 3% to 8% byweight.
 20. A coating fluid for enhancing permanence of ink jet imagingon non-porous and semi-porous substrates, the coating fluid comprising apolyethyleimine or an ethoxylated polyethyleimine polymer, an acrylicpolymer, dimethylethanolamine in an amount sufficient to preventinteraction between the polymers, and a mixture of methyl ethyl ketoneand alcohol, wherein the methyl ethyl ketone is present in an amount of20% to 50% by weight.